Apparatus for casting thin walled hollow cylindrical inserts

ABSTRACT

A mold for casting thin-walled hollow cylindrical inserts from hazardous materials for use in warheads, rocket motors and pyrotechnic flares. The apparatus comprises a plurality of disposable presized tubes fitted within each other, and spaced apart so as to form mold spaces or chambers which are filled with a hazardous material, such as explosive. Upon curing the tubes are peeled off leaving thin-walled tubular inserts.

United States Patent Silver et al.

[54] APPARATUS FOR CASTING THIN WALLED HOLLOW CYLINDRICAL INSERTS [72] lnventors: Wallace E. Silver, Ridgecrest; Jack Sherman, China Lake, both of Calif.

[73] Assignee: The United States of America as represented by the Secretary of the Navy [22] Filed: Nov. 18, 1968 [21] Appl. N0.: 777,211

[52] US. Cl. ..86/l R, l8/DlG. l2, l8/D1G. 43,

[5 I Int. Cl. ..C06b 21/02, F4 1 b H00 [58] Fieldol'Search ..l8/5;25/l28 K, 128R; 86/1,

[56] References Cited UNITED STATES PATENTS 138.035 4/1873 Mclntyre ..25/l28 K 1 May' 9, 1972 Gorman ..25/l28 K UX Miller ..25/l28 K Sokolowski ..86/20.5 Hain ..25/l28 K White et al. ..86/20.l Copenhaver et al. ..18/DlG. 30 Anspon l 8/DlG. 30

Primary ExaminerStephen C. Bentley Attorney-Edgar J. Brower and Roy Miller ABSTRACT A mold for casting thin-walled hollow cylindrical inserts from hazardous materials for use in warheads, rocket motors and pyrotechnic flares. The apparatus comprises a plurality of disposable presized tubes fitted within each other, and spaced apart so as to form mold spaces or chambers which are filled with a hazardous material, such as explosive. Upon curing the tubes are peeled off leaving thin-walled tubular inserts.

1 Claim, 5 Drawing Figures PATENTEUMY 91912 SHEET 1 [IF 2 INVENTORS. WALLACE E. SILVER JACK SHERMAN ROY MILLER ATTORNEY.

PATENTEDMAY 9 1972 SHEET 2 OF 2 FIG. 3.

FIG. 2B.

APPARATUS FOR CASTING THIN WALLED HOLLOW CYLINDRICAL INSERTS GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION At the present time when a thin-walled hollow cylindrical explosive-type insert is required for use in a multilayered warhead, rocket motor or pyrotechnic flare, it is either machined from a cast or pressed solid cylindrical piece or cast around a solid mandrel in a metal mold and then mechanically ejected. The machining of such inserts to the tolerances required by contemporary ordnance is time consuming, costly and hazardous. The cast piece very often shrinks around the center mandrel making ejection of an undamaged insert from the mold very difi'icult. The present invention provides thinwalled, hollow, cylindrical inserts of hazardous materials which do not require machining or mechanical ejection and safety considerations are minimized. Only the physical mixing of the uncured materials used need be done remotely.

SUMMARY OF THE INVENTION The present invention relates to a mold for casting thinwalled hollow cylindrical inserts from hazardous materials.

It is the general purpose of this invention to provide a mold for casting inserts of a hazardous material for use in multilayered high explosive warheads, solid propellant rocket motors or pyrotechnic flares. Another object is to provide an insert which meets tolerances of great precision thereby providing a savings in time and money. Yet another object is to provide a means for manufacturing inserts of hazardous material which reduces the hazard in handling by personnel to a minimum. Further objects of this invention will appear as the description proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an exploded view in section of an assemblage constructed in accordance with the present invention;

FIGS. 2A and 2B are vertical sections showing the assemblage after filling with hazardous material;

FIG. 3 is a single configuration of a thin-walled explosive insert formed in the apparatus of FIGS. 2A and 2B; and

FIG. 4 is an unfolded multilayered configuration of thinwalled explosive inserts formed in a multi-tubed assemblage (not shown) in accordance with the present invention.

DESCRIPTION OF AN EMBODIMENT Referring now to the drawings there is shown in FIG. 1 the unassembled elements of an embodiment of this invention which comprises an outer cylindrical disposable tube and a smaller diameter inner disposable tube 11, open at their two ends and of suitable length positioned one within the other. The tubes being such that the inner wall of the outer tube and the outer wall of the inner tube defines mold space or chamber 12 into which hazardous material is cast. The space formed by the walls of tubes 10 and 11 for this embodiment was onehalf inch thick and the tubes were 2 feet long. A base plate 13 which forms the bottom of this device is made of aluminum or other suitable material and is provided with a metal ring 14 which is superimposed upon said plate 13. The plate used herein was three-fourths inch thick and the ring one-half inch thick. Ring 14 forms the bottom of mold space 12. Tubes 10 and 11 are concentrically fitted onto plate ring 14 to form an annular cross section of mold space 12. Ring 14 is one-half inch thick and tube 11 is of such a size as to fit snugly to the inside of ring 14 and tube 10 which is larger fits snugly to the outside of said ring so as to form a mold space or chamber one-half inch wide. A hose clamp with set screw for tightening (not shown) is used to secure the tubes to the ring. A funnel means designated generally by numeral 15 fits onto the top of said tubes 10 and 11 for directing or funneling the material into mold space or chamber 12 defined between tubes 10 and 11. The funnel means comprises a conical cap 16 of metal such as aluminum which fits over the top end of the inner shell 11. Cap 16 is provided with a rabbeted groove 21 which fits over the top end of inner tube 11 and a straight-walled annular collar 17 provided also with a rabbeted groove 22 which fits over the top end of outer tube 10. In the present embodiment the cone is about five-sixteenths inch thick and the collar is about three-sixteenths inch thick. A metal spacer ring 18, the

width of mold space 12 (in this instance one-half inch) is pro-.

vided for positioning over the top of cast material 19 when mold space 12 is filled with said material 19.

In operation a predetermined quantity of a hazardous material such as high explosive, propellant composition, or pyrotechnic is poured or cast into mold space or chamber 12. The mold is gently vibrated as the casting continues to insure that no air bubbles are formed in the material. Funnel means 15 is removed after the mold has been filled and spacer ring 18 is then inserted on top of the material between the walls of the two tubes forming space 12 to insure that the insert is of concentric cross section with uniform wall thickness. After the material is cured, the cardboard comprising the tube walls is peeled off by hand, leaving the desired thin-walled insert as shown in FIG. 3. All parts of the mold are reusable except for the disposable material forming tubes 10 and 11 which in this embodiment was cardboard. The walls of cardboard tubes, 10 and 11, which form mold section 12 are coated with a very thin layer of silicone rubber spray designated 19 which prevents adhesion of the cured cast material to the cardboard surfaces. The silicone or other suitable release agent may be applied by painting or spraying.

With this mold both hollow cylinders of hazardous material and other thin-walled objects of greater complexity can be precision cast at a minimum cost and with great safety. It is possible to cast objects to a wall thickness of one-sixteenth inch and to a tolerance of $0.005 inch. Of course, in order to obtain such precision the shrinkage characteristics of the material used must be taken into consideration when using the mold. Multiple thin-walled inserts may be cast as shown in FIG. 4 in a multi-tubed assemblage (not shown) in the same quick and efiicient manner. Auxiliary equipment such as machine tools and ejection fixtures are unnecessary.

Propellant compositions comprising both castable doublebase and composite compositions can be molded in this device for rocket motors requiring complex grain structure. A typical double-base composition comprises nitroglycerin, nitrocellulose, aluminum and' ammonium perchlorate. A typical cast composite propellant composition consists essentially of ammonium perchlorate, a metal such as aluminum and a binder such as polyurethane.

For modern pyrotechnic flare designs a castable material comprising sodium nitrate, magnesium and Laminac polyester has been used. This invention has been very successfully used in casting thin-walled hollow, cylindrical explosive specimens. The following data for a few explosive specimens is given in the tabulation below:

Average wall thickness, inch Average v i -------A-- outside 1 inch 3 inches 5 inches 6 inches 3 inches 1 inch Specimen diameter, Weight, Density, from from from from from from designation Composition in. gram g./cm. top top top bottom bottom bottom 111. {40.04% Binder. 6.037 2, 750 1.557 0.315 0.313 0.313 0.314 0. 311 0.316

0.25% Cab-o-Sil 2 HVI 1V 1 1 38.57% Binder. 4. 895 2, 553 1, 54.) 0. 340 0. 342 0. 344 0. 344 U. 343 0. 352

0.51% Cab-0 Sil 61.22% lIMX 38.30% Binderv 6. 034 2,780 1. 540 u. 310 0.301) 0.311 (1305 o. 315 0. 30::

0.48% (Tab-o-Sil.

HMX Cyclmelramelhylenelelfanilfa plosives, pyrotechnics or the like; said mold consisting of mme Binder Styrenated polyester resin. a first tube formed of cardboard open at each end.

EpX 47 2 Sold by American 20 a second tube smaller than sa1d first tube formed of card- Cyanamid board open at each end positioned within said first tube; Pymgemc P'E a mold space defined by the inner wall of said first tube and New warheads are requiring new explosive loading techniques because of the more stringent need of quality and reproducibility. This device provided explosive inserts of varying explosive formulations averaging a wall thickness of from 1 to 3 inches.

The preferred silicone rubber sprayed on the inside of the mold space was divinyl tetramethyl disiloxane. Other suitable silicone rubbers may be used to prevent the material from sticking to the walls of the mold.

What is claimed is:

l. A mold for use in forming thin-walled hollow inserts from hazardous material comprising propellant compositions, ex-

the outer wall of said second tube; the walls of said space being coated with silicone rubber;

25 an aluminum plate provided with an aluminum ring the thickness of said mold space superimposed on said plate having the bottom of each of said tubes concentrically fitted on said ring to hold said mold in an annular cross section of the thickness of said ring;

30 an aluminum funnel means positioned on the top of said tubes for directing uncured material into said mold space;

said funnel means comprising a conical cap positioned over the top end of said inner tube and an annular section positioned on the top of said outer tube. 

1. A mold for use in forming thin-walled hollow inserts from hazardous material comprising propellant compositions, explosives, pyrotechnics or the like; said mold consisting of a first tube formed of cardboard open at each end; a second tube smaller than said first tube formed of cardboard open at each end positioned within said first tube; a mold space defined by the inner wall of said first tube and the outer wall of said second tube; the walls of said space being coated with silicone rubber; an aluminum plate provided with an aluminum ring the thickness of said mold space superimposed on said plate having the bottom of each of said tubes concentrically fitted on said ring to hold said mold in an annular cross section of the thickness of said ring; an aluminum funnel means positioned on the top of said tubes for directing uncured material into said mold space; said funnel means comprising a conical cap positioned over the top end of said inner tube and an annular section positioned on the top of said outer tube. 